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How dangerous is flying in a single-engine plane?
Some people consider flying small planes very dangerous. Just how dangerous is it to fly in a light single-engine plane? For example, how does the fatality rate compare to driving a car, riding a motorcycle, etc.?

Usually, folks argue: the less props, the higher the risk. Interestingly, the same folks do not consider gliders to be more risky.

@Krumelur Due to the simplicity of most essential glider technology technical failures are quite rare. Just about all of the risk there is human factors related.

@Krumelur The converse argument certainly favors gliders: The more engines you have the greater the chance of an engine failure. Gilders are thus inherently safe, as they have no engine to fail :-)

The major factor in ga crashes is the pilot. So pick a good one if you fly in a ga aircraft.

No problem. Every pilot considers himself or herself above average.

@Krumelur: there's an old adage for private planes that goes something like, "when the first engine fails, the second will fly you to the accident site."

My grandpa has told me that one. Are we talking two-stroke or four-stroke engines?

@xpda I am the only driver I trust to drive in the snow, because you all are crazy! :)

@CGCampbell, you do have a point.  :)

Also remember that a glider is PLANNING to have no engine... they fly with the assumption that they should never be further than a single glide from their location to the runway and plan accordingly. Single engined aircraft will almost certainly get out of glide range of an airfield at some stage of their journey.

And gliders have glide ratios of anywhere from 20:1 to 50:1 or more. Most airplanes are in the 10:1 to 12:1 range. And then there's the worst glider in the world with a glide ratio of 1:1.

I get this question a lot from people who are apprehensive about flying with a private pilot.  I'm afraid I won't be reducing these fears in any way.  Let's review some general statistics during 2008.  Note - these stats aren't specific to light or single engine aircraft:

NTSB reported there were 1.21 fatalities per 100,000 flight hours for private aircraft (Part 91 operators).
NHTSA reported there were 1.26 fatalities per 100 million miles travelled by automobile

We can equate that to about 2 million hours (estimating an average speed of 50mph). This gives us 0.063 fatalities per 100,000 driving hours.
Private aircraft have a fatality rate about 19 times greater than driving.  It is also true that a majority of the accidents that occur are pilot error (71%) and could have been prevented.
There are risks involved when taking to the sky as a private pilot and understanding these risks is part of the continual learning process.  The key to safety is performing careful planning, keeping current and proficient, knowing when to cancel flights or turn around and not to exceed your capabilities or the capabilities of your aircraft.

Was the question specific to single engine aircraft?  Can we generalize that single engine = private aircraft?

@Michael: not a bad question. There are also a lot of incidents involving light twins and asymmetric power flight (e.g. training, engine failure, etc.). Are these cases substantial enough to make a significant difference between single engine accident data, compared to all private operations?

I remember reading several years ago that twin piston planes had a similar fatality rate to crop dusters. It may have changed since then.

Could you cite your source? I'm curious/hoping they'll have numbers for commercial flight operations as well.

@JeffBridgman sure - NTSB: http://apps.bts.gov/publications/national_transportation_statistics/html/table_02_14.html and NHTSA: http://www-fars.nhtsa.dot.gov/main/index.aspx

Although the risk may be 19x over driving, 1.2 deaths per 100,000 hours still seems awfully safe to me.  I don't imagine I could amass 100,000 hours in my lifetime, no matter how much I flew, and if I did, I'd expect to die only once? Sounds like a pretty safe deal to me.

@abelenky 100,000 hours is 137 years (give or take) of two hours every single day. Put differently, you'd die exactly once after just over 113 years of flying two hours every single day (113 y * 365 d/y * 2 h/d * 1.21 = 99,813 flight hours). Yes, seems reasonably safe. Statistically, of course. In practice, with Launchpad McQuack around, you are safe for far, far longer than that.

But I don't want to die in 137 years! This is probably the best number, though - people fly when they shouldn't, make bad decisions, and fly badly... but they also drive when they shouldn't, make bad decisions, and drive badly.

As @voretaq7 hints in his answer, this approach seems too simplistic. For people considering flying versus driving (as I am), a comparison of hours is not really a good baseline, as the constant between modes of travel is usually the distance. Also, I think that though the number of passengers on a plane is also masking the true level of risk. Far fewer people fit in a car when it crashes. If cars were to fit more people then I think this statistic would be comparably skewed. When considering a mode of travel, I expect the overall probability of a fatal incident would be comparably lower.

Since Geoff took the devil's advocate position, I'll play cheerleader.
If you look at the statistics another way, like AOPA does, you'll find that General Aviation has "about one-sixth as many accidents on a per-vehicle-mile basis" compared to driving.
Or to put it another way I'm 6 times more likely to get in a car accident driving to the airport as I am doing an equivalent number of miles puttering around in the pattern (my drive isn't that far - it's only worth a few laps around the pattern).

So now I've gone and left you with two essentially contradictory answers, both based on statistics from the same source, and both equally valid from a cold, unfeeling, numerical standpoint. But the answer isn't important.
Geoff and I are both really making the same point:

Each flight is as safe as the pilot wants to make it.

The pilot comes up with a plan for the flight, gathers as much information as they can about the weather, the aircraft, the route, etc., and then assess the situation.
They weigh the risks and determine whether or not the level of risk in making that flight is acceptable.
The statistics are useful. Most pilots I know spend a lot of time thinking about them (mainly why they're so lousy, and how we can make them better), but as a passenger remember they lump in the professionals with the students, and the conscientious pilot doing a thorough preflight with the one who haphazardly kicks the tire as he's climbing in for a 500 mile trip as his first flight in 6 months.
Which kind of pilot are you flying with?

As an aside I have a delightful personal "Risk Management" story I'd be willing to share if there's interest in setting up a site blog at some point. It involves two legs of a flight, a mechanical issue, and two radically different risk profiles.

The argument could be made that each flight and each drive is as safe as the pilot wants to make it.

"Each flight is as safe as the pilot wants to make it."  That's not true.  There are some risks that are not controllable by the pilot.  Those we either accept or stay on the ground.

@SkipMiller You are always accepting some level of risk when you undertake any activity - even walking along the street on a sidewalk is not free of risk. When you've eliminated the risks within your control you've maximized safety to the extent possible when undertaking an activity. The only way to eliminate the risks outside your control is to not engage in the activity, which is always an option, but it would be so boring :-)

Complete agreement with that.

@SkipMiller If the pilot "accepts risk or stays on the ground" then by making that choice it is indeed within control of the pilot.

@SteveV.: not really as far as driving goes as there are far more drivers on the road that I can't control compared to the ones (me) that I can.

I'm not sure passenger-miles are the best measure here - even light aircraft aircraft at 140mph (Cessna 172 taken as typical) are generally travelling 2-5x faster than the average speed of a car (in 45,000 miles I've averaged 32mph in my car, and I do a lot of long-distance). That's not to say passenger hours is flawless, either.

@JonStory hourly accident rates are certainly useful, but passenger-miles are more universally comparable across modalities: the gross distance from Farmingdale to Albany doesn't change, but times can vary widely between aircraft, train, and car. (Time varies within modalities too: A Cherokee will take much longer than a Meridian to make the trip.) A better measure might be the "per trip" accident rate, but that's much harder to quantify.

Oh I agree that passenger-mile is more comparable for putting multiple transport methods side by side in terms of overall safety (how many people die for how much useful travelling?) but in terms of "How likely am I to die undertaking this activity", hours are more useful than miles. Especially when a single engine aircraft isn't usually used for pure transportation (ie you probably aren't trying to get very far)

Because I'm both a single engine pilot and motorcycle rider, the way I explain risk to new passengers is as follows:
Daytime flight over non-mountainous terrain:  Like riding a motorcycle with full gear.
Daytime flight in instrument conditions or over mountainous terrain in clear air:  Like riding a motorcycle with only a helmet.
Night flight over non-mountainous terrain:  Like riding a motorcycle with a helmet but no headlight.
Night flight in instrument conditions over non-mountainous terrain:  Like riding a motorcycle at night with a headlight but no helmet.
Night flight in instrument conditions over mountainous terrain:  Like riding a motorcycle at night with no helmet, in the rain, over the speed limit.
Any flight in which the pilot says 'watch this sh*t' - Like riding a motorcycle at night with no helmet, over the speed limit, while drunk.
Flying a single engine airplane is more dangerous than 'driving to the airport'.

lol, don't know that I completely agree, but I will say, I'd never fly with a pilot who I've ever heard utter a phrase that starts with "Watch this!"

I wish I could cite sources, but at an AOPA Safety Seminar, I remember Phil Boyer saying something to the effect of "we need to stop saying that driving to the airport is more dangerous, unless you're riding a motorcycle. Statistically, flying an airplane is about the same risk statistically as driving a motorcycle," and then he went on to cite the actual percentages and all that.  Again, I don't have sources for stats, but I think its fitting with your analogy :)

@Canuk That would only apply to private flights though

@Cloud well yeah, the OP was asking about "flights in a small plane" which I assumed he was talking about flights in small, private aircraft.

I would probably re-phrase this question as how much 'riskier' flying in a light single engine airplane is as opposed to how much more dangerous one is.
When comparing General Aviation flying in a small, single engine, normal category airplane to a larger, transport category airplane (e.g. A320), both aircraft are subject to essentially the same hazards, but Scheduled air carrier service does have far less risk (the adverse consequences if a hazard is not properly mitigated) than do GA aircraft.
By the numbers, it is undeniable that GA aircraft have far higher rates of both nonfatal and fatal accidents.  Aircraft Owners and Pilot's Association (AOPA) estimates that in 2017, GA pilots flew approx. 25 million flight hours that year. The NTSB estimates that for the same year, there were 10.617 GA accidents and 1.977 fatal GA accidents per 100,000 flight hours. As a yardstick, the death rates per 100 million passenger miles applied to all passenger vehicles on the road is somewhere in the neighborhood of 0.6. The airlines, with only four deaths over the past 10 years of operations, don’t even chart.  The NTSB also concludes that the death rates of airline passengers per 100,000 flight hours are statistically nearly zero.
The tremendous accident rate of general aviation can be attributed to a number of factors:

Part 25 Transport Category Aircraft used by air carriers are certified to a much more stringent set of standards by governmental regulatory agencies.
Scheduled Air Carriers (SAC) operate far more stringent maintenance programs than are required by law for GA aircraft.
Scheduled Air Carrier flights are planned and prepared by teams of people specializing in meterology, fuel management, flight planning, air navigation, etc.
SAC flights are crewed by pilots who hold a far more stringent Airline Transport Pilot's Certificate and often have far more flight time logged in all kinds of conditions than do their general aviation counterparts.  In addition they are required to be type rated on the aircraft they fly, which includes annual recurrent training and must hold a first class medical certificate to work as airline pilots.
SAC flights are conducted under Instrument Flight Rules and always under the guidance and observation of ATC.
Transport Category airplanes are, for the most part, turbine powered and pressurized, allowing them to operate above most kinds of adverse weather and offer effective anti-icing/de-icing equipment and procedures, both before departure and during flight.  They generally are multi-engine aircraft with performance guarantees, even with an engine inoperative, giving them much greater redundancy.

General Aviation aircraft operated under Part 91 recreational flight rules generally don't offer such things for their passengers.

Pilots often hold no more than a private pilot certificate in the category and class of the airplane they are flying and have only themselves to rely on in order to plan, prepare and execute a flight.
The airplanes they fly are either maintained by an FBO in which they
were rented from or by the owner, often consisting of only an annual
inspection for owner operated aircraft.
They are often flown into smaller, remote and uncontrolled airports and operated around other similarly untrained pilots.
Small, single engine GA airplanes operate at lower altitude in weather, good or bad, and may have limited redundancy, or takeoff and climb performance, given local conditions.
recurrent training for most GA pilots is limited, often just to a biannual flight review with the only real emergency training check they have received being when they did their practical exam to receive the pilot certificate so many years back.
Some GA pilots have a very limited mechanical aptitude or fundamental understanding of how an airplane works and how to troubleshoot problems in an emergency.
An opinion I have, is that the most dangerous thing in an airplane is a pilot that simply doesn’t know what they don’t know ie simply unaware of what the real hazards are or how challenging an aspect of their flight will be until they get there.

Because of this, it's easy to understand why there is much less risk flying the airlines as opposed to on a GA aircraft.  That being said a capable, well informed and knowledgeable GA pilot can conduct a flight in a light airplane in a very safe and in a competent fashion, mitigating the risks faced on the flight with good planning and judgment as well as sound operating practices.
It is well documented throughout history of aviation that over 85% of accidents are attributed to pilot error as opposed to mechanical faults or other phenomena.  And, a quick review of general aviation accidents will reveal that the lion’s share of them are attributed to this.  Most of the NTSB entries for GA accidents are filled with foolhardy, boneheaded, and incompetent decisions by the pilot, exhibition of hazardous attitudes in their aeronautical decision making, caving to peer pressure or other external influences, and otherwise doing things that they just should not be doing in an aircraft.  These things can be insidious; nobody wakes up one day, and decides to go do something reckless and die in an airplane crash. But accident chains of poor judgment, hazardous circumstances have a way of coming together to cause an accident which, if the same person were watching the events from afar, would wonder why anyone would do something so crazy.
“Aviation itself is not inherently dangerous. But, to an even greater degree than the Sea, it is terribly unforgiving of carelessness, incapacity, and neglect.”
-A.G. Lamplugh

Is this including all GA or just light single engine planes?

Those figures are inclusive of all GA, at least, according to AOPA.  You will also note from that data that single engine aircraft represents ~75% of the general aviation fleet.

Flying in a small aircraft is far more dangerous than other methods of transportation (see statistics in other answers). I would not recommend it unless you have a positive reason to use a small plane. Thrill seeking or taking aircraft flights for "fun" is not a good idea from a statistical point of view. I fly strictly for practical reasons and I would recommend that as a general policy for anyone considering flying either as a pilot or a passenger.
Flying in a small aircraft is not as dangerous as base jumping or scuba diving.
Pilot nature, skill and attitude have a large impact on the danger in a flight. Most people get killed in small planes because the pilot did something that was either foolish (like taking shortcuts in the pattern), reckless (flying into storms) or because they panicked. If a pilot acts cocky, that is a huge warning sign.


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Is it technically viable to reintroduce sleeping berths?
The airlines are always trying to jam more passengers into each plane. I'm smaller than today's average, and I'm still often uncomfortable in a standard Economy seat.
It occurred to me that in the current design, there's a great deal of space wasted over the passengers' heads. And that many of us passengers already do our best to sleep through flights.
Hence my question: Is there any reason an airline couldn't introduce a cabin in which some or all passengers travel in a reclining, rather than sitting, position? Seems to me that  it would be more comfortable (except for claustrophobes and those who really need to work during the flight). The enclosed space would inherently reduce some of the risks of passengers being thrown around in turbulence or an emergency landing; safety belts (or cargo restraint webbing? I'm not sure I'm joking) could handle the remaining risk.
No, I don't really think it would be commercially viable ... but I'm wondering whether folks who actually Know Something about aircraft safety and loading think it's technically viable.

I'm not sure this is exactly what you're looking for, but there's Air New Zealand "cuddle class". That doesn't do much for packing more people in though.

I'm seeing Fifth Element's (a movie) cabin in the space plane that takes Korbin Dallas to the Fhloston Paradise Cruise Liner.... of course we'd need the sleepy time gas as well... I'd pay for that.

"It occurred to me that in the current design, there's a great deal of space wasted over the passengers' heads."
Well, you definitely confirmed your previous statement that you're smaller than average with that part. - haha - In regional jets, I literally have to duck the exit signs in the aisle and I'm only 6'1". The higher ceilings of wide-bodies are very welcome as they are for tall people.

No objection to a high-ceilinged aisle. But it feels like there should be better ways of packing humans which are no more claustrophobic -- perhaps less.

I've always been interested in "standing seats" -- for short flights, like LAX<->SFO, I would be totally fine standing, and I imagine you could put more people in. I realize that turbulence, and seatbelts are still a problem, but there's nothing preventing me from being seat belted to a wall.

While not an aircraft I just took the megabus from Glasgow to London overnight. There is a lot that can be learned from out of the box thinking. When done overnight there won't be a need for food and they have seat belts and netting to hold you in while you sleep. Obviously some more concerns to consider including regulations but I think you might see it one day.

There was once a type of railroad sleeping car called a Slumbercoach where sleeping compartments alternated high-low, nested into each other.  It put 2 compartments about every 7.5 lineal feet of car.  The rooms even included a bathroom that didn't require you to fold up the bed (not necessary in airline service but the formfactor of railroad cars left them with a lot of useless space). The trick would be airframe mods to put a window in every compartment.  Like all sleepers it converted from day seating to night bed.

Some airlines already offer sleeping facilities, by taking advantage of the A380's tremendous size:

A double-bed suite on Singapore Airlines

A first-class seat on Emirates

A first-class seat on Qantas

That top bed looks very tempting, but I dread to think how much it costs!

Etihad's First Class has a cabin. The cost is I think 7-10 grands whereas in economy people pay $1000.

What do the people in the bed up top do for take-off/landing?

@cpast There's an armchair in the suites, too.

@Danny Beckett has already covered the more luxurious variants of reclining seats very well, but I wanted to answer your point about "wasted space". The space above the passengers' heads is currently used for hand luggage, so you'd need to find somewhere else to store that. But even if you solved that, there are a few major issues to consider:

The maximum number of passengers in a plane is limited by the number and size of the doors (for evacuation, you need to be able to get all passengers out in 90 seconds in case of a crash landing). If you put more people into the cabin you would need more/larger doors, so depending on the design of the plane it might not be feasible to try and cram more passengers in. (see also: unusual seating arrangements)
The "evacuate in 90 seconds" rule bites you in a second way: In an emergency, getting out of a standard airline seat, running down the aisle, and out the door is (reasonably) quick. If you had to climb down from your bed under the ceiling first, it would take much more time.
The rules for passenger safety during a crash (or severe turbulence) are pretty strict. Any reclining chair can be put upright (and designers assume that passengers will have sufficient warning of a crash/turbulence to put their seats upright, and be reasonably well strapped in and protected), but if you're lying down there isn't a good way to stop you from bouncing off the walls or ceiling (or, even if you're wearing some kind of belt, from hitting your head on said walls or ceiling). In short, lying down is not a safe position to be in in an emergency.
From a practical point of view, I don't think flying while lying down in a cramped space is all that comfortable, especially for long-haul. You would have to climb down into the aisle to walk around or go to the toilet, you would have to eat/read/watch TV while lying down, not to mention the extra difficulty of climbing over the person in the berth next to you if there is more than one berth on each side of the aisle. (thank you to @Peter Kämpf for the additional input!)

In conclusion, it's currently not technically feasible to design an airplane cabin which would meet aviation safety rules with bunks above the passenger heads.

You may want to add that even without an emergency, people walk around all the time. Berth width would necessitate two each side of an aisle - how do you get out from a window berth? And then there is meal service - would you want to eat while sitting or while lying down in a small tube?

Made me think a system where the space for entry and exit is in the ground facility. People get in, machines move the pods to plane, the plane travels, machines off-load the pods, and then people get off. This might be legal if the pods were capable of floating and light enough to fall at a speed they can survive, if the pilot pushes "emergency eject pods" while airborne. An airbag system would make for slower falls, protect from impacts, and allow floating in the sea until rescue. The plane would only need the space for visiting toilets one at a time. Obviously no walking around or eating.

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Other than the rest areas for the crew - what else is in the 'attic' of an aeroplane?
So I am seeing some information about crew rest areas in an aeroplane which typically just sit above the passenger cabin.
In the image of the a350 XWB for example you can see those areas in the front and back of the aeroplane.
However, what is happening in the rest of the aeroplane - is the 'attic' just sitting empty?

Image borrowed from  FreeMan's answer here

I'm pretty sure that's where they keep the snakes.

The “attic” is mostly unused. The area above the passenger cabin is also called the crown area. Some aircraft do use part of it for crew rest areas. That area can also used to route electrical wiring, hydraulic lines, air conditioning, and pneumatic lines.
Wikipedia A300 image

Volker Gollnick photo

Wasn't there a movie where the crown area was used by special forces soldiers to move the length of the plane unobserved by hijackers?  Completely hollywood of course.

@Criggie Air Force One of "Get off my plane!" and steven-segal-dying-after-10-minutes fame

Is this universal? I'm sure I've travelled on 3-4-3 planes that had a big dip in the ceiling above the middle seats, where one presumes stuff could happen.

Steven Seagal's was Executive Decision, Air Force One was Harrison Ford. :) Great 90's action.

There was also a lot of crawling around in vast empty spaces in David Fincher’s Flight Plan starring Jodie Foster.

@CGCampbell OMG what a mistakea to makea. Course it was. But it was in fact executive decision where they were crawling around in the attic. I just got my hijacked-plane movies mixed up.

@Criggie Yeah, I'm pretty sure that false ceiling between the cabin and the crown is not strong enough to support people - it's not built to be load-bearing.  Kind of like crawling around in HVAC ducts like you see them doing in so many movies.  Most likely result is you falling through the ceiling...

A potential crossover question between here and Movies.SE... "Have there been more hijackings in real live or in movies ?"  and which is more successful.

The "attic" elsewhere is overhead luggage bins, as on most airliners.  See the fuselage cross-section (circle, top right) and #47 in this cutaway of an A350-900, which also notes the crew rest compartments fore and aft.

So what you're saying is that the crew are considered carry on luggage... :)

Sure!  I bet Dick Rutan and Jeana Yeager felt like that too, after nine days!

This would mean that in the crew rest areas there are no overhead luggage compartments?

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How are conflicts between pilot flying and pilot not-flying over aircraft control resolved?
A question about the "my aircraft" protocol led to several answers that explain how the pilot flying (PF) can delegate control to the pilot not flying (PNF).
It also seems that a pilot (e.g. returning from a break) can assert "I have control" without the other pilot first offering control.
From what I've read, unlike with ATC communications, the exact phrases used vary from airline to airline and are not the subject of rules or guidance by authorities such as the FAA. It also seems that in some airlines, some pilots are more casual about the use of standard phrases.
The only fixed idea seems to be that as long as both pilots have uttered some complementary phrase, both should now be aware that a transfer of control has occurred, and to whom.
This led me to wonder: under what circumstances can the PF refuse the PNF's request, how would they phrase this and does the other pilot or pilots always defer to the senior pilot?

The whole idea behind the policies and procedures for transferring control of the aircraft between the pilots is so that everybody is always on the same page.  Somebody always needs to be flying the aircraft.
If I want to hand control over to the other pilot, and he doesn't want it/can't take it, he would simply explain why not.  I have never seen standard operating procedures (SOP's) that explain how to refuse, as simply saying no or unable should let the other pilot know that there is a problem and should be the beginning of a conversation about it.  On the other hand, the SOP's do cover the scenario where the other pilot doesn't respond.
This is why there is always a challenge/response as part of handing off control.  If the other pilot were incapacitated and I didn't realize it, I would say "You have the flight controls" (or whatever phrase that the SOP's require) and wait for his response.  If they didn't respond, I wouldn't just blindly stop flying the airplane and assume that they are.  Instead, I could say it again or look over at them to see what was going on and figure out what the problem was while continuing to fly the airplane.
Now, to request control from the other pilot (rather than requesting them to take control), I would simply skip the first part and say "I have the flight controls" and they should respond with "You have the flight controls."  Again, it's a challenge/response situation so that everybody is on the same page.
In either case, the captain is the final authority and can always override a request.  Airline policies are all very clear that if there is a disagreement, the captain has the "tie breaking" vote.

Just curious, has there ever been an instance where a pilot has said "You have control", and then realized the other pilot was incapacitated afterwards? It seems that the close proximity of the two pilots to each other in the average cockpit would keep this from happening.

@flyingfisch If a pilot has a sudden massive heart attack/stroke/etc. and simply slumped over during a busy time, it might not be noticed right away because your attention is focused elsewhere.  Has it happened?  I'm not sure, but they train us for the worst case scenario in lots of areas, either because it has happened, or because of the possible severe consequences if it were to happen.  In either case, it doesn't cause problems in the "typical" case, so why not do it all the time?

ah, i didn't think of that. maybe it would have helped in this scenario?

@flyingfisch it's hard to say whether or not it would have helped in that accident. There were no CVR's back then, but the captain was probably already flying and there wouldn't have been a reason to change that so early in the flight.  That means that there wouldn't have been the challenge or expected response....

Instead of one pilot being completely incapacitated, it would seem to be a more relevant risk that he's simply momentarily zoned out and/or focusing on something else. Without an explicit response one might easily end up in a state where both pilots are awake, responsive, and convinced that the other guy is flying the plane.

@HenningMakholm good point, didn't think of that.

@HenningMakholm Agreed. That's why I say in my answer that if they didn't respond that I would ask again and look over at them to see what was going on. :)

@HenningMakholm that is how the RNLAF lost one of their AH-64D Apache helicopters in Afghanistan. Frontseater transfered control ("you have control"), but the backseater replied "No, standby". The frontseater didn't hear the message correctly and assumed it was a confirmation. With both pilots assuming the other was in control they soon crashed. If the frontseater would have reconfirmed the transfer of control (you have control) as per SOP, the accident could probably have been prevented.

@HenningMakholm "Subtle Incapacitation" is another risk to bear in mind (sometimes it's not obvious the other pilot is in no condition to fly). Positive exchange of controls can help mitigate this (if the other pilot responds with "Who am I? Why am I here? I can't be a pilot - I'm afraid of heights!" you'll probably not let go of the controls. OK maybe that example is not so subtle...)

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Can a V22 Osprey operate with only one propeller?
Can a V22 hover with only one propeller rotating under power? If yes, is the other prop feathered like in an airplane or still rotating sans power? Also, can the Osprey hover if one prop happens to fall off?

Key parts of this answer (which may make this question a duplicate): "It is possible to drive the two rotors of the V-22 Osprey from a single engine..." and "On aircraft with two distant rotors, it is vital to have both rotating, as if one slows or stops the aircraft is unbalanced to the extent {that} it crashes."

The V-22 Osprey has an elaborate gearbox, clutch, and cross-shaft system by which both rotors can be driven from one engine.
Both rotors must always be turning for flight, but there are multiple layers of redundancy to keep that the case.

However elaborate the system may be, if one engine fails, it only takes a failure of one critical component in the system for the other propeller to lose power.

@Jpe61 - sure, but that is like saying if one engine fails, and then the other engine fails, its a problem. Two critical failures is hard to overcome.

In a military aircraft this would not be as unimaginable as one might think. Shrapnell or projectiles may very well take out both the engine on one side and the power transmission lile from the remaining engine.

@Jpe61 - yes, and military aircraft don't have the same safety requirements as civilian aircraft.

@JonCuster your point being? V-22 Osprey is a military aircraft.

@Jpe61 - survival of two major failures is not a large consideration for military equipment. Once one engine has failed, the cross-connection is the backup. If the cross-connection fails, well, people die and that is expected for military action. The decision on how-safe-is-safe stopped there at two critical failures. For a civilian aircraft a different decision, such as adding some additional safety factor, might be done.

@JonCuster: Indeed, in a civilian aircraft, if adding additional safety systems makes the aircraft slightly heavier and thus less maneuverable, that's considered a tolerable annoyance in exchange for reducing risk.  Making a military aircraft less maneuverable increases the risk of failures induced by enemy ordnance, and that increase in risk may exceed any reduction in risk the systems might otherwise have provided.

@JonCuster do you honestly think personnel is considered expendable in military scenarios? I war there will be losses for sure, but military will go to great lengths to protect personnel extreme even.

@Jpe61 No, you're treating this thing as an airliner. Look at helicopters: there are a large number of gearbox, bearing, and rotor failure modes which are unrecoverable.  If you substitute a Chinook for a V-22, you have ideally similar risk in takeoff and landing, but your cruise phase gets fixed-wing handling, so you've lowered your overall risk.

@user71659 what the hell?

Definitely not. The operating propeller applies huge rolling and yawing moments. In hovering flight there is nothing to counter these except the other propeller.

I thought the Osprey could complete a flight while maintaining forward motion.  Taking off and landing while rolling across a runway.  There would be rudder and differential braking.  I think the question is: would the rudder authority be sufficient for a high speed landing on a long runway?

@AnonymousPhysicist The question is about hovering flight. With sufficient airspeed it should be possible to maintain control.

@AnonymousPhysicist The Osprey's rotors are so large that they would strike the ground in the forward flight position if it tried to land.  They will sometimes do a rolling takeoff/landing with the nacelles tilted 45deg, but not much lower than that.  I do not think the Osprey rudders are sized to maintain controlled flight with one rotor inoperative or missing.  They rely on the cross shafting, gearboxes, and clutches.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
If I own land, can I create a private helicopter landing spot for my personal use?
If I own land(in the U.S.), can I create a private helicopter landing spot for my personal use? Would I have to register with the FAA or some other government agency?

Related: If I own land, can I create a private runway on my property for my own use?

Also related: What does "NON-COMPLIANCE WITH FAR 157" mean for an airport?

Helipads have the same issue as runways (as mentioned in the comment above:  If I own land, can I create a private runway on my property for my own use?  )
Generally, local regulations (State, County, City) are what can make it difficult.  As part of planning to create a huge Amazon complex in NYC, Bezos wanted to be able to land his helicopter there.  With enough $Billions at stake, he was able to get approval:
https://slate.com/business/2018/11/amazons-new-york-hq2-helipad-jeff-bezos.html
Although, that deal ultimately did not go ahead.
The other thing that can be an issue is insurance for a helicopter that might not allow off-field landings.
It would be much easier for example, if it were on your own farm, when you use a helicopter to spray crops.
Essentially, the FAA doesn't care, as long as it doesn't interfere with other airspace.  But, local regulations might.

"Essentially, the FAA doesn't care, as long as it doesn't interfere with other airspace", right, but the airfield has limitations.


text:
Will the pilot bear any responsibility or be investigated if a passenger dies due to a medical emergency that the captain refused to act upon?
In the case of medical emergencies among the passengers, the pilot generally have the final say on whether or not the plane will be diverted. While this is true, I'm wondering what kind of responsibilities/liabilities will the pilot(s) face if they refuse to divert and the passenger died as a result? Will they be investigated and scrutinized by the FAA, their airliner, law enforcement, or any other governmental bodies? Or are they exempt from such responsibilities since it's their job to decide? Let's say the deceased passenger died of a normal condition, for example cardiac arrest or heart attack.
According to this post, deaths inflight are not extremely uncommon. An answer to this question also states the events following a passenger death on an aircraft.
However, they say nothing about the (potential) investigation and scrutiny of pilots if they refuse to divert for an ill passenger. Will there be any such investigations?

Could you give any indication as to why the captain might make the decision not to divert due to a medical situation on a plane? I downvoted due to the extremely speculative nature of this question, I cannot for the life of me come up with a scenarion where the pilot would refuse to divert without a solid, safety related reason in a case with an ill passenger.

@Jpe61 The point of my question is with an out-of-the-ordinary pilot. Normal pilot's won't do that, but you can't say no pilot would. The most "normal" (i.e, not unethical, just mistaken) reason would be that the passenger is originally not in a life-threatening situation, the aircraft was already delayed, and so the pilot decided to continue. But after over halfway into the flight, the situation worsens and became life-threatening. Before landing, the passenger's dead.

Ask law SE. I assume family would sue airline (where the money is), but you ask "responsibility" which seems more on criminal side, so complex: most rules "will not apply" (they do not have criminal delegation. Ask Law SE -- Also it depends on jurisdiction: countries have different view on priorities and procedures.

Definitely a law question more than an aviation question. This is probably going to be a discussion of negligence and duty of care, but honestly, I'm not sure there's a case on point. Without a specific case that addresses a very similar scenario, there may not be a solid answer -- just the arguments for and against that the lawyers would make.

"...the pilot generally have the final say on whether or not the plane will be diverted." The Pilot In Comman has the final say. Always, no exceptions.

Most aspects would be better answered at law.se, here is some food for thought only, and I hope better answers will be posted. I'm neither a pilot nor a legal advisor.
Your question "Will the pilot bear any responsibility or be investigated if a passenger dies due to a medical emergency that the captain refused to act upon?" is not meaningless, of course the decision to not divert may be mistakenly taken by a well-intentioned pilot, due to the different elements to be assessed.
However such situation is unlikely: The pilot (in command) won't be alone for deciding. They will be discussing with the ground flight dispatcher, assisted by a doctor, possibly a lawyer, and other experts. The dispatcher and the pilot-in-command will agree on the final decision. This restrict the risk of a wrong decision. Even if a diversion is a costly operation for the operator, they won't take the risk of having their image degraded in the long term for "not willing to spend a few dollars and save a life".
It's the opposite, they may want to divert even if there is no real benefit for the person requiring medical attention, because article 17.1 of the Warsaw convention presuppose damage liability of the operator for any in-flight injury or death of a passenger, regardless of the reason, thought only up to a certain amount.
If a wrong decision is taken, then the operator employees, including the pilot-in-command and the dispatcher, and their management may be prosecuted, and sentenced if faults are proven. These employees have no specific privileges or protection.

There are different aspects to consider:

When you write "pilot" (as pilot flying), you should use "pilot in command" (PIC). For commercial carriers, the PIC, who has the rank of Captain in some countries, Commander in other, represents the operator authority for important decisions like a diversion.

When you write "responsible" you should use "liable" as except specific cases, everybody is accountable of their actions. Legal liability can be of two kinds: For the action and/or for the consequences of the action:

Sanction for the author of an action breaching a legal obligation (penal/criminal action by the State).
Victim compensation for the consequences of a fault, regardless of whether the law has been breached (civil/litigation action by the victim).

The base for liability and compensation is Warsaw Convention. Liability is not limited to the crew, the crew as been trained by an employer and receives instructions from a manager.

When risk is considered by the PIC, it is not limited to risk for the passenger in medical emergency, but is extended to the risk associated with the diversion:

Maybe the only possible diversion airfield has no medical structure and, this may reduce the passenger chances to be medically assisted.

Maybe the landing will be difficult due to weather conditions and the life of all passengers might be at stake.

In a commercial air transport environment, the crew doesn't act alone, they have a counterpart on the ground, the flight dispatcher  or Operations, who can provide advice and instructions.
For more see What is the role of the flight dispatcher? How do the dispatcher and the flight crew interact?.
The liability will now be shared. Operations will ask for a medical advice and decide what to do, possibly assisted by the operator's lawyer.

The crew will also ask for medical expertise on-board. A doctor on-board has likely no (legal) obligation to offer or accept to provide assistance, and if they do the legal liability is not very clear. These two elements may depend on the State of registration of the aircraft and/or the nationality of the doctor. The in-board doctor may or may not suggest an immediate landing. This is taken into account too when determining iability.

A diversion is a huge cost for the operator, this cost won't be covered by the passenger insurance. So the decision is not limited to well-being considerations. On the other hand not diverting, even for valid reasons, may have a huge commercial impact.

An operator has an overall obligation to take care of the passengers and their safety. It is liable for any damage. But there is apparently no law like "the flight termination is required in case of death-threatening situation".
In addition, there are no international laws, so an answer to your question maybe State-dependent, or even may depend on which territory or water area is currently overflown:

So-called international obligations are the results of bilateral or multilateral treaties like Chicago Convention, and, for liability, Warsaw Convention and Montreal Convention. These treaties are obligations for the States, and are implemented by signatories into their own law in order to be applicable to their citizens. This implementation can lead to local variations.

In some countries everyone can be sanctioned for not providing assistance to someone whose life is threatened, e.g. Non-assistance à personne en danger in French law. This individual obligation has a precedence higher than most other collective or professional obligations.

In the context of air transport, the latter obligation of assistance specifically means:

A French doctor in an aircraft registered in France must offer help in case of medical emergency (this is not limited to doctors, other professions are concerned).

The PIC can be taken to a court for a breach of this single obligation, no need for the existence of a professional fault. However again, it must be proved the PIC had the elements to evaluate the situation and the decision to not land wasn't motivated by valid reasons.

All in all, diverting is a PIC's decision based on their own judgment, taking into account all elements. As for any decision, the PIC will be liable and must demonstrate this decision was a good one. Think of the emergency ditching in the Hudson: Is it a good decision? should I try to land at the closest airfield to prevent drownings? After the facts the PIC had to explain and prove this was a sensible decision. The fact this decision was sensible had likely a huge financial impact for paying the enormous associated costs and damages.

Thanks to @Jpe61 for mentioning the difference PIC/Captain.


text:
Do Cargo flights carry anyone other than the crew?
This question talks a bit about the crews that are involved in a commercial cargo flight, but I'm wondering if Cargo flights every carry other sorts of people on their flights?  Say, a photographer to take pictures of operations for advertising or something.  Or maybe one of the crews kids who want's to see what Mom does or something like that.  Or, perhaps there's even another person who's normally there?
If they do, here's a couple bonus questions:

Do they have jump seats?  And are they in the cockpit, or in the cargo hold?  (Just in general, I assume different planes have different setups).
Are there any regulations regarding this?

As I remember, at least one jump seat is a regulatory requirement for the purpose of conducting flight checks. Also, if an FAA inspector shows up at the last moment for an unannounced check, he must be given the seat even though a jumpseating pilot is already in it. There were some problems back in the 1990s with FAA inspectors doing this when their real purpose was personal travel and the spot check merely an excuse.

Been done. See the James Harriet books.

...commercial cargo flight... can be tricky to define. I booked flights every once in a while on Alaska Air cargo flights out of Juneau, AK, to Seattle, WA. Craft were generally 737s with only 6 rows of passenger seats.

I have heard there is a regulation (under US FAR) that only employees of the airline (or possibly, other airlines with reciprocal agreements) are allowed as passengers; ordinary civilians, family members, etc would not be allowed.   Can't find the reference, though.

Yes, cargo aircraft are like other aircraft in that there is generally at least a jump seat available. Especially larger aircraft will also have additional jump seats, a lavatory, and a galley. This area can be used for relief crew, or other crew that are just deadheading.
There are exceptions though. The upper deck of the 747 is larger than just the cockpit, even on the cargo versions. There is more room in the back for additional crew. The An-124 and An-225 also have additional space for crew behind the cockpit. The extra crew can be loadmasters, navigators, mechanics, or other functions that can make it easier to operate in and out of airports with less services available.
Here is the upper deck of a 747-400F:

I spent many an hour crammed into the jumpseats of 727's (they have 2, both in the broom closet sized cockpit with 3 crew members). I worked as a cargo handler at the FedEx hub in Memphis and at the time we could book any open jumpseat.
When i clocked out at 4am there were a couple hundred planes just about to depart for destinations all over the world. It was awesome, but alas, no more. It even continued after an off duty pilot with a hammer decided to try and hijack one of our planes from the jumpseat. But 19 jerks ended all that on Sep 11, 2001. There are still non-crew persons in the jumpseat but now you have to have a good reason to be there. It's mostly deadheading pilots but anybody that has an "operational need" for the company can jumpseat. So if they need a mechanic somewhere or something like that they can go.
As far as what jumpseats there are it differs by aircraft. Like i mentioned the 727's had 2 terribly uncomfortable seats in the cockpit. The dc10's I've flown on had one in the cockpit and either 2 or 4 against the bulkhead facing backward. [Think Tom Hanks in Castaway. That was very accurate, you're staring at the first set of cargo containers behind a safety net the whole flight.] In the 747-100 there were about 10 airline seats in the upper deck and two bunks at the back. The 747-200's were the nicest. They were formerly passenger planes so the upper deck still had the first class seating.

Some airlines operate their aircraft in a combination of freighter and passenger aircraft. See here for the floor plan of KLM's Boeing 747-400M Combi. It has a large cargo door at the rear fuselage for loading freight containers.
Humanitarian relief flights have an obligation to carry journalists along if they wish. Some governments have instituted a policy of transparency so the press may observe first-hand where the goods are delivered to.

Yes actually I have an uncle who flew on a c-130 cargo plane to Alaska that was carrying jet fuel if you consider that cargo. The plane he was on was refueling jets in the sky. So yes sometimes they do carry people on planes with cargo. And it usually when its only necessary.

If they have got a technical work, don't they belong to the crew? And fuel is not cargo.

Well if you consider fuel a cargo then the answer would be yes.

If the C-130 was loaded with supplies for a air-drop, most would consider the supplies to be "cargo". Since the fuel was intended for aerial refueling, then I'd think that would be considered cargo as well.

@FreeMan You do have a good point.

@anshabhi On freighters, loadmasters are often carried to facilitate the loading of freighters when there would not otherwise be a qualified loadmaster available as part of the ground support people. Since they have no inflight function, they are not required air crew.

@anshabhi The test as to whether fuel is to be considered in with the cargo, i.e. included in the zero fuel weight for purposes of weight and balance, is whether it is legally available for use by the airplane carrying it during the flight. For example, ballast fuel, i.e. fuel carried to keep the c.g. within limits, is treated like cargo even though it is in the aircraft's fuel tanks. Obviously, in a fuel emergency, you could use that fuel. However, to do so might take you outside the legal c.g. limits.

To be fair, any flying C-130 is going to be "carrying jet fuel", seeing as it's a turboprop aircraft.


text:
Why are rules regarding the use of oxygen masks by commercial pilots often ignored?
I was reading an article recently on the effects of rapid depressurization when I came across this tidbit:  According to FAR 135.89.2, aircrews of part charter craft flying pressurized aircraft above 35,000 MSL are required to have one member of the aircrew on oxygen at all times.
I've seen a few videos of charter pilots flying planes around FL410 and I don't recall any where they had masks on (admittedly, there are not a lot of small business jet charter flight videos out there.) In general, though, it seems the rule is ignored.
So, why isn't the rule followed?  Why don't pilots seems to wear oxygen masks in situations the regulations say they are supposed to?

Addendum:
In the original, unedited, version I made the mistake of thinking FAR 135 applied to airliners, when that's clearly 121 that applies to airliners...
Still, in FAR 121.333 it states that the rules around airmasks for commercial airline aircraft (over 30 passengers) require that pilots always have oxygen when they are either a) over FL410 or b) over FL250 and one of the flight crew leaves the flight deck.
Of these conditions, it seems condition A is followed by default (flying under FL410), but condition B is often ignored.  So I'd be curious why that part of the rule isn't followed as well.
Basically, I'm asking why pilots generally don't wear oxygen masks when regulations require that they are supposed to.

A big thanks to Zach Lipton for pointing out my error to me.

Did you mean 35,000 feet?

Sorry Jay, VTC.  Your question states "aircrews flying pressurized aircraft above 25,000 MSL are required to have one member of the aircrew on oxygen at all times".  The FAR does not state that.  It's therefore unclear what you are asking.  I assume that the title and the body both mean to reference FL350.

@Simon I fixed it, I now talk about the actual FARS I link instead of....whatever I was doing (it was early in the morning when I wrote the question, I jus made some slip ups.)  If it's still unclear though, please tell me and I'll edit it again.

@Federico I did?

@Federico The focus was actually on FAR 135, because it's more strict.  But I included 121 in the question because it seemed related.

@Federico Decided to change the title to just be more inclusive overall.

@Federico Eh, it was a worthwhile improvement.

Just an anecdote, I heard that there was an FAA inspector in the NE USA who regularly would hop on board an airplane which just landed after flying from Europe above the altitude where oxygen was required and looked at the oxygen gauge.  If it was full, he had some questions along with a violation for the pilots.  This led to some pilots simply depressing the oxygen test button during the flight in order to bleed off some of the "excess" oxygen.  It's very hard to make people do something when they don't feel that it's needed....

@Lnafziger The last sentence of your comment sums up the consensus of the culture during the 1980s and 1990s. We did always don the mask and check it for operation during the preflight. We never donned it enroute unless we had an FAA inspector jumpseating.

@Terry I have a few questions about that if you want to head over to the hangar...  Just ping me if you go and I'll send a questions or two.  http://chat.stackexchange.com/transcript/message/31580674#31580674

The rule you've found is under part 135 of the FARs, which generally governs commuter and on-demand operations like many charter flights. Most commercial airlines, such as those flying large passenger jets on regularly scheduled routes, are part 121 operators, which follow different rules.
For part 135 operators, there are a few caveats. First, above 25,000 MSL, there is an exception to the oxygen requirement if "each pilot has an approved quick-donning type oxygen mask." If the aircraft is so equipped, masks are only required above 35,000 MSL or when one pilot has left the cockpit.
The rules for part 121 operators are a bit different and can be found in 14 CFR 121.333. Under these rules, if quick-donning masks are available and the aircraft has more than 30 seats or a payload capacity of more than 7,500 lbs, oxygen is not required at or below FL410 unless one pilot has temporarily left the controls.
Since the majority of videos you may see online probably involve two pilots flying a large part 121 airliner (or one under a foreign regulatory regime, where different rules apply), oxygen masks would not be required in most of the situations where cockpit films are released.
That said, I found this article, which may be of some interest: Study: Pilots Ignore Oxygen Regulations. It cites the results of a survey conducted as part of a student's master's thesis which concludes that the rules are ignored quite often and that there really aren't effective ways to enforce them either:

The compliance numbers for Part 121 respondents were higher, with 39
  percent reporting always using oxygen when required above 25,000 feet
  and 48 percent above 41,000 feet.
Part 135 respondents were nearer the Part 91 results, with 21 percent
  saying they always use supplemental oxygen when only one crewmember is
  at the controls above 25,000 feet and 18 percent continuously using
  oxygen when flying above 35,000 feet.

So for part 121 operators, the primary time when the regulation is relevant is when one pilot has left the cockpit above FL250. The article goes on to discuss some of the reasons pilots may not follow the regulation and whether the regulation makes good sense. Some pilots on the PPRuNe Forums discussed the rules here (before they were changed to FL410) and also here. One author notes, with regard to donning masks during bathroom breaks, that "there is probably no more violated FAR in US operations than this one." Several reasons are posited in those threads, among them:

Some non-military pilots do not receive decompression chamber training, and so do not have an appreciation for the effects of severe hypoxia and its dangers
This practice would use up much of the cockpit oxygen supply, especially on long-haul flights, leaving less available in the event of an emergency (some information on how long oxygen supplies tend to last)
The expense and time involved in topping off oxygen tanks all the time if they were routinely used.
A desire to reduce the complexity of single-pilot operations during breaks, not wanting the remaining pilot to complicate things by donning the mask and adjusting audio settings accordingly instead of focusing on the aircraft
In some cases, restowing the masks may require maintenance personnel after the flight, which is impractical
The same rules do not apply under many other regulatory regimes, which leads people to conclude they are unimportant

Note that some pilots discuss using the masks routinely, both to ensure that their operations are as safe and legal as possible, and to give the crew practice and experience in donning and using the masks so they will be comfortable with them in the event of an emergency.

Yes, you're right, I meant charters and I meant over FL350...  Anyway, I've edited the question to fit with what you brought up, you might consider editing your answer to refelct that (not that you have to, just thought I'd point it out to you.)  Thanks for straightening me out :)

There's a lot of good information here, but very little of it answers the question of why pilots ignore this specific regulation. Could you perhaps summarize the main 'theories' from the PPRuNe forum discussions?

I remember once when jumpseating on freighters back in the 90's seeing the FO put on his mask as the captain went to the bathroom. I must have had a panicky look on my face because the flight engineer quickly explained the rule to me. Out of numerous jumpseat trips that was the ONLY time I ever observed anyone put on a mask except during pre-flight.

@Pondlife  Was thinking the same thing, now that it's been done, I'm going to mark this the answer.


text:
In general terms, is a Constant Speed Propellor equiped aircraft more expensive to maintain?
I've been looking at possibly buying a used Mooney M20 or a used Cessna 172.  One of the big differences between the two is that the Cessna is a fixed prop, and the Mooney is a constant speed propellor.  While CSPs sound really nifty and efficient...I can't help but wonder if they would be more expensive to maintain.  Both in terms of regular maintenance and just the fact that it has more parts that can break.
Is a CSP more expensive to maintain than a fixed pitch prop?  And why? If you can include some numbers that relate to the planes mentioned, that'd be cool too...

Is it more expensive to maintain? Yes, if it needs maintenance. Just like anything else that's a little more complicated. For example if you have retractable gear they are more expensive than fixed if they need it. Regular inspections and routine maintenance can keep those costs down though. The other side is that if something does break, it may break more than the prop assembly, for example if the engine is overspeed because the prop governor fails then you have much much more cost.

@RonBeyer -- there's also the issue of scheduled maintenance...

Having just had an annual done on my C-177B Cardinal, that portion was very minor (I don't think it was even called out on the hour rate sheet). The oil changes also don't seem to be much more frequent but I never maintained a fixed pitch plane myself.

@RonBeyer So you're saying maintenance cost on a CBP is more or less $0?  And the only per hour cost I'll incur is an amortized hourly charge for an eventual inspection?

A 172 an M20x are two totally different  planes.  What do you expect to do on your typical flight?

the M20 is not a 172 with a fixed-pitch prop!

@acpilot You guys are getting a little caught up in the example.  I'm aware a 172 v. a 177 would have been a better comparison, I just happened to be looking at an M20c and a 172n when I wrote the question.  Try not to read too much into it.

@JayCarr then edit the question to be a better comparison. any of the constant-speed cessnas versus the 172

Yes, they are more expensive because they are more complex.  I would not avoid buying a plane simply because it has a CS prop because, in the grand scheme of airplane ownership, CS prop maintenance has a small impact on your hourly cost.  Maybe ~$1/hr for a piston single with repetitive ADs.
Now, the maintenance of a CS prop can range from a simple visual inspection of about \$100 USD to a complete replacement of the prop (up to \$15,000 USD, maybe more for large props).  An owner will likely not do an "overhaul" when the prop reaches TBO but will instead opt for an IRAN (Inspect, Repair As Necessary).  This is typically a little cheaper than a full blown overhaul and, from a practical perspective, extends the life of the propeller as an overhaul would.  At some point you'll end up grinding blades and balancing the prop but that's not annual maintenance.  I've seen the cost quoted at around \$1,500 USD for a high performance piston single IRAN which comes to less than $1/hr for a private owner.
All in, a CS prop only adds a small amount to the hourly operating cost.  In my opinion, the performance gains are worth the cost in most cases.

So, basically, if I perhaps put a little money into a "maintenance fund" for every hour I fly the plane, I can just put aside a few dollars for every hour flown and cover the cost of an IRAN?  How often does an IRAN turn into an overhaul though?  It seems like the cost could be variable...

Short answer, yes on the fund. If there is corrosion in the hub or a crack in the hub the prop shop will probably recommend an OH. Shop around with some prop shops and see what they think. I'd check to see if the Mooney has a "no-AD" prop. Many have been switched to no-AD already. Not a dealbreaker but it's a good negotiating tool to beat down the price a little. The gear system maint on the Mooney will probably cost more than the prop maint over a given period (still not awful, just plan for it). Also, prop governors can be pricey to OH (~1500us @ 2000hrs if I recall) so keep that in mind.

Also, for what it's worth, the manual gear and flap systems on the M20C-F are great.

You'll have to forgive me, but what is a "no-AD" prop?

A propeller without any aiworthiness directives tied to it. Some props have an AD requiring an inspection for cracks every 100hrs (or some short interval). Props without that AD do not require periodic inspections. I don't know the details of the inspection but it does require a mechanic to spend time on inspection and paperwork which translates into billable hours.  If a crack is found you need to repair or replace the offending component which = even more expense.

One thing about constant speed props that nobody has mentioned is that there is also a cost savings. a fixed pitch prop is like a one speed transmission, where constant speed prop can be adjusted for the current need (climb vs cruise). This means that, at least in theory, you can either go faster at a given rate of fuel flow, or burn less fuel at a given speed.
Whether or not this makes constant speed props cheaper in the long run probably depends a lot on the plane and the frequency and style in which you fly.

Perhaps, but this is all starting to remind me of the problem with early (current gen) hybrid petrol/electric cars.  They cost so much more that by the end of the time you had the car, you still hadn't made the money back in  supposed fuel savings.  I think I'd almost rather a 172 with a mogas conversion if I was really keen on cutting fuel costs.

ACPilot hit it on the head in a general sense but ill add to that a bit to more directly cover the direct parts of the question as well as the aircraft in question. I don't know which Mooney you are looking at but if you are also looking at 172's I can assume you are looking at the M20C's D's and E's possibly J models (although the C's and D's are closest to the 172). The older variants of these planes along with being CS props are subject to an AD that requires 100 hour eddy current inspections. This makes these props more expensive to maintain than even their non AD counterparts.
As mentioned the CS props can be more expensive simply because they have moving parts. But for this particular case the AD can add quite a bit of cost. It should be noted that there is a Non-AD prop available for these airframes and many have been converted.

A fixed prop is relatively low maintenance. Basically, all you do it file out cracks for maintenance.
A constant speed prop has moving parts. There is usually an oil linkage. Usually, a constant speed prop has to be overhauled at regular intervals like the engine.

Filing out cracks is generally frowned upon. A cracked aluminum prop is a wall decoration. However, small knicks that have not led to cracking can be repaired by filing and polishing. Over time the prop does need to be rebalanced as well.


text:
What do they use to de-ice aircraft and runways on snowy days?
One of the answers to this question mentions how runways are usually in need of de-icing on cold days (which makes sense), and as anyone who has ridden an airplane on a cold day knows, planes need de-icing too.
What I'm wondering is a few things:

What is used to de-ice a commercial aircraft?
What is used to de-ice a runway at a large airport?
Do the two fluids effect each other at all?  Meaning, when an aircraft drips de-icing fluid onto the runway, does it cause any interactions or problems?

EASA published a report on the issue of aircraft anti-ice and runway de-icing products interacting: http://www.skybrary.aero/bookshelf/books/1347.pdf

I wonder how difficult it would be to build electrically heated runways.

@SimonRichter someone asked that questions on this stack once, if you do a search I recall there being a pretty good answer.

What is used to de-ice a commercial aircraft?
De-icing fluids are used which are made of ethylene glycol (EG) or propylene glycol (PG) in addition to other ingredients.

What is used to de-ice a runway at a large airport?
Airports use different types of materials, e.g. potassium acetate. Safegrip ECO2 is a brand which is popular.
Runways can also be deiced using normal techniques like salt and snowplows etc.
Do the two fluids effect each other at all? Meaning, when an aircraft drips de-icing fluid onto the runway, does it cause any interactions or problems?
I do not think that there is much or any damage to a runway from the de-icing fluid. If something is bad for solid concrete, how it can be good for fragile aluminium?
Research shows that the residuals left on the airplanes cause some issues. Those are described below.
Effect of runway de-icing fluid residuals on airplanes
There are some studies that show the runway fluid having some adverse effects when combined with de-icing fluid residuals on airplanes. They state:

Runway deicing fluids contain potassium acetateor potassium
  formate-based fluids (deionizing salts). When these fluids combine,
  the separation of the anti-icing fluid thickeners may be enhanced,
  leading to a more rapid formation of the residue.

Effect of airplane de-icing fluid residuals on airplanes
However, de-icing fluid residuals on airplanes can freeze and cause damages to flight controls. More information is here.

The bulletin linked by usernumber in the other comment, http://www.skybrary.aero/bookshelf/books/1347.pdf, indicates that splashes of the runway de-icing fluid can reduce effectiveness of the type-IV aircraft anti-icing fluid if not cleared by applying hot water or type-I de-icing fluid first.

@Farhan - If you could add what Jan is referencing to your answer I would gladly mark it as the correct one.

@JayCarr I've updated my answer.

So, the ingredients used to de-ice seem to be like the antifreeze used in cars?

@verve - Similar. Ethylene glycol pretty much is automotive antifreeze. It's very poisonous to humans and wildlife, so propylene glycol (much less toxic but slightly less effective) is favored in certain areas. There are other de-icing fluids as well based on other alcohols.

They test whether the runway needs clearing with a vehicle with acceleration sensors to check the grip when the driver steps on the brakes.
Airports will try to avoid using salt or glycol to clear the runway for environmental and maintenance reasons (salted sludge spray will corrode exposed metal on the plane) though they can be very effective for keeping the runway clear in moderate temperatures. Preferring the mechanical plows, blowers and sweepers to clear the surface.
Some airports also use grit to provide a grippy surface for the plane.

Salt is almost never used due to the fact it's corrosive to many metals.

Snowplow train at Salzburg.


text:
What is the difference between a high bypass turbofan and a low bypass turbofan?
I see some questions on the site that talk about the relative positives and negatives of a high bypass turbofan (HB) vs a low bypass turbofan (LB).  But I don't see anything explaining what actually makes a turbofan engine HB or LB?  I assume it has to do with the ratio of air that is bypassing the compressor stages and just going through the fans.  But what ratio makes an engine HB v. LB?  And why was that ratio chosen?

Please note: I am not looking for usage cases, I am looking for differences in design specifications.

May be related to the development of higher bypass ratios

Something on the order of between 4 to 5 to one is the limit between high and low bypass. I just did some Google search on several engines and that is what I came up with.

The first turbofan, the RR Conway, had just a bypass ratio of 0.25. It was designed for installation into the wing root of airplanes like the HP Victor bomber or the Vickers V-1000 transport project, so RR strived to keep the diameter small. Of course, back then nobody distinguished low- and high-bypass engines. The P&W JT-3D, which powered most of the second generation of jet airliners (Boeing 707 and DC-8), had a bypass ratio of less than 1.5.
But when the new generation of engines (GE CF-6, JT-9D) with bypass ratios of around 5 were developed for the first generation of wide body jets, marketing needed a term to make clear that this was a new generation of engines, and the high-bypass ratio engine category was born. Generally, the threshold is around 5, but note that some CF-6 versions have bypass ratios as low as 4.24 and still fall into the high bypass ratio category. Therefore, Wikipedia sets the limit at a bypass ratio of 4.
There is no technical difference between a low- and a high-bypass engine, and the limit is arbitrary. The jump in bypass ratio from 1.5 to 5 brought significant improvements in specific fuel consumption and noise reduction, but part of the technical progress was also from better materials and aerodynamics, which allowed higher compression ratios and turbine entry temperatures.
Now, almost 50 years later, we see the first engines with bypass ratios above 10 entering service. Designs are being readied with bypass ratios of 12, so marketing will need a new word to describe those creations. With "ultra high bypass" already taken by the unducted fan crowd, the search is on.

So there's no structural difference you can point at (other than the arbitrary 4:1 ratio), that might easily distinguish between the two?  It's really just a loose marketing term with no meaning rooted in actual engineering?

@JayCarr: No, even most low-bypass ratio engines use two spools, and a few with bypass ratios above 4 have only a single spool (Lycoming ALF502)

@JayCarr: The new generation in the mid- to end-sixties had a substantially lower specific fuel consumption due to the higher bypass ratio, so it is not all marketing. But, yes, the term is an arbitrary definition, and some fuel saving was also due to better materials, better internal design and so on which also benefited the low-bypass engine crowd (just compare the P&W F100 with the J79 or even the J57). Remember that the J57 became the JT-3D when the fan was added ...

The Lycoming ALF502 page doesn't say it is single-spool. It does not mention is would be two-spool either, but the mention of separate high and low pressure turbines, and the mention of free power turbine in its turboshaft T55 ancestor suggests two-spool. Of course WP can be wrong, but do you have a better reference then (the links in WP are both dead)?

They can't jump to Ultra High Bypass! They skipped Very High Bypass!

They could use "I cant believe it's not bypass."

@JanHudec: I was always under the impression they achieved the speed reduction for the fan by the gearbox only, but this cutaway drawing suggests you are right. This would make the ALF502 a real two-spool geared turbofan, something like the P&W 1000. I should rewrite the comment using the Turbomeca Astafan.

@DavidRicherby Except that it is bypass?

According to Wikipedia Low bypass means lower than 2, so there's also a middle region (Medium Bypass? :p )
https://en.wikipedia.org/wiki/Category:Low-bypass_turbofan_engines

I was guessing, but according to Wikipedia, they're actually called Medium bypass engines if the bypass ratio is between 2 and 4

@ROIMaison: Yes, indeed Wikipedia has a medium bypass category, but this is not widely used - such fine grained differences are of limited usefulness. Why not refine further into low medium and high medium? At some point it becomes pointless.

There is no particular ratio at which the engine becomes a 'high' bypass, though the it is generally taken to be around ~5:1. The reasons are more historic than technical.
The first large scale development of the high-bypass turbofans was spurred by the USAF's CX-HLS competition, which lead to the C-5 Galaxy. The requirements of the competition (range and fuel efficiency) lead to the development of a new generation of engine by GE and PW, which developed the TF39 and JTF14E respectively. GE won the contract with the TF39 engine, which had a previously unheard of 8:1 bypass ratio.
PW figured out that it better develop a high bypass engine itself or lose the market and developed the JT9D, which had a 5:1 bypass ratio. This engine was the first widely used engine with high bypass ratio (the previous engine had bypass ratios in the range of ~1 or so) and necessitated a special mention, which came to be called high-bypass engines, once it became widely used, especially in the Boeing 747 (Ironically, it was the two losers of the CX-HLS competition PW and Boeing, which won the immediate race in civil aircraft).
Joe Sutter acknowledged the effect of the CX competition in the development of 747:

I should add that fostering large high-bypass engines was all that the USAF C-5 competition contributed to the Boeing 747, as my new airplane would be called.

Not to be left behind, GE developed the CF6 series with bypass ratios of 6:1 and RR developed the RB211-22 which had a bypass ratio of ~5:1. Due to these, the ratio of around 5:1 (or >4:1) is usually taken as the dividing line between the 'high' and 'low' bypass ratio turbofans.

"Bypass" in this context is how much air transits the actual fan stage and is used to directly generate thrust, vs. how much air transits the fan stage and moves into the compressor stage to be burned in the engine.
Low-bypass turbofans don't use a lot of air for thrust; most of the air that transits the fan stage is routed into the engine, compressed, combusted, and exhausted like a standard turbojet.  High-bypass turbofans route more air outside the combustion core, so the spinning fan generates most of the thrust (rather than the actual engine).  In this case, the turbojet core of the engine is used (mostly) to generate engine rotation, and the fans generate most of the thrust.

The question does not ask for the physical differences between HP and LP turbofans. It asks for the mathematical ratio that puts and engine into the HP or LP category.


text:
What are the V-Speeds used during a normal takeoff in a multi-engine airplane?
This is what I know:

$V_1$ is the takeoff airspeed after which the aircraft must take off, no matter what happens after $V_1$ has been reached. That's the easy part (I think).
$V_R$ is the rotation airspeed

Are there any other $V$-speeds?
What I'm specifically curious about:

Is $V_1$ related to runway length?
Is there an absolute maximum $V_1$ for each aircraft type? If so, can it vary based on conditions (takeoff weight, density altitude, etc.)
Are there circumstances where $V_1$ is higher than $V_R$? If so, does that mean that $V_1$ is never called on a normal takeoff? (this is the case for most light aircraft, but I guess the whole concept is not applicable in that case)
What exactly is $V_2$?
Is there a $V_3$? (and so on)

Anything else worth knowing about $V$-speeds?

$V_1$ is takeoff decision speed.  It is based upon:

Runway length
Temperature
Reduced thrust takeoff
Takeoff weight
Takeoff flap setting

If $V_1$ is higher than $V_R$, then (as far as I am aware), $V_1$ will be adjusted to be the same as $V_R$.  You have to make the decision to takeoff by the time you rotate, so it does not make much sense to have $V_1$ higher than $V_R$.
$V_2$ is takeoff safety speed.  During a one engine inop takeoff we would accelerate to and climb at this airspeed to our acceleration height (a height we could level off at and be safe from obstacles while we further accelerate).  We also referenced certain flap transitions on takeoff to $V_2$ (e.g. $V_2+15$ - flaps 0)
To address the rest of the question, $V_1$ and $V_2$ are primarily used in large aircraft.  In light twins you also need to be aware of $V_{MC}$.  $V_{MC}$ is the minimum controllable airspeed with an engine inop.  In particular you do not want to be slower than this airspeed during climbout in case of engine failure.

A single engine takeoff is pretty scary in a 747!  (You might want to use "one engine inop"). :-)

Stretching my memory, but I'll try, and others can correct what I get wrong. Think 'balanced field length'. Given an engine failure, $V_1$ is that speed at which if you abort you will be able to stop at the very end of the runway. $V_1$ is that speed at which if you choose to fly you will lift off at the very end of the runway. $V_1$ is that speed which if you are above and you abort you will go off the end of the runway (Kalitta 747 freighter a few years back tried to abort at $V_1+30$).
The longer the runway, the higher your $V_1$. Enough runway and $V_1$ can exceed $V_2$, but that doesn't mean anything because you're going to rotate at $V_2$. If you choose to stay on the runway after $V_2$, you begin moving into an area limited by max tire heating. Maybe you can say that max $V_1$ is the max tire speed? I don't know.
Can't remember a $V_3$.

VMO and VMC are both important
VMO = Maximum Operating Speed, a structurally safe maximum speed which varies with altitude. For example with an emergency descent in a B777 the VMO is 310kt IAS, but in level flight it is 330 KIAS. As you climb the air thins so the true airspeed increases.
VMC = Minimum Controllable Speed with one engine inoperative, gear retracted with CG at most rearward limit, bad engine at idle but not feathered (if propellor)

How is the VMO relevant to the question?


text:
Is the pilot supposed to take over control in an emergency situation, even if he is originally the Pilot Not Flying?
This question basically stems from Air Algerie Flight 6289 1, 2 , which crashed mainly due to pilot error combined with engine failure. One thing in particular that intrigued me is that in both Mentour Pilot's Youtube video and the Wikipedia page, it was stated that the captain's last minute decision to take control was a bad decision that contributed to the crash.
He was originally the Pilot Monitoring, or the Pilot Not Flying (PNF), and the first officer was the Pilot Flying. Immediately after the engine failure, he declared that he is going to become the Pilot Flying, told the first officer to let go of the controls, but didn't know what to do himself.
My question is, is this a bad decision simply because the captain wasn't prepared to handle the situation (since he was chatting with the purser and skipped the briefing), or is it a general rule of thumb to not initiate a change of roles in the middle of an emergency (impending stall in this case)? Is it generally applicable that the captain should not take over, or is it the opposite, that the captain actually should take over the controls in an emergency?

Normally the Captain would let the FO continue flying and execute the PF's emergency drill and the capt will do the PNF's tasks.
This is what they train for in the sim. If you're PF, you remain PF.
If the FO was smart, he/she would be constantly drilling all those procedures to death whenever there was free time, so when the time comes, they just go into automatic mode and their mind is free to think ahead. That's how new pilots can outperform expectations.
If the FO was falling behind or starting to freeze up from becoming mentally saturated, the Capt would then intervene, call out "my controls" and take over the PF's tasks while the FO takes over the PNF's tasks. And if the FO is completely freaked out and out of the picture, or just doing things completely wrong, the Capt would simply start doing everything him/herself and tell the FO to read a book or just stick to the radio or something. This assumes a Captain who, you know, actually belongs in command.
Air Algerie was both a training problem and a cultural one. Developing world operators can tend to be 50 years behind the times when it comes to crew interaction and command, that is, following Crew Resource Management principles (by behind the times, I mean, for example, where the FO's job is to shut up and follow orders, like in the West in the 50s). And, in some countries, where you get ahead by your connections, pilots may get promoted to Captain because of who they are. The airlines recognize this problem, which is why you see so many expat Commonwealth/European/American Captains (retirees mostly) flying at these operators.

Great answer, so usually if assuming both pilots are professional and competent, they would not switch roles. I didn't know that Air Algerie was that unadvanced. I also didn't know that there was once a time where the captain had absolute authority over the FO. That sure didn't work out! :) Thanks for the answer, by the way.

The old phrase to describe copilots was "gear puller". Things changed with the advent of CRM. I knew of an Iraqi Airways captain taking a CRJ type course. He failed his check ride. He EXPECTED to be passed anyway, because that's how things went back home, and was indignant, threatening the instructor/examiner. He was whisked away and told never to come back. You wouldn't get me on any Middle Eastern (or Russian or Chinese or South American) airliner without an expat capt, even today.

As Anas Maaz pointed out below though, US Airways Flight 1549 is an opposite case. The FO, Jeff Skiles, is certainly competent and outstanding. He obviously did not freeze, panic, or freak out, even though in such dire circumstances that they were facing. The captain, Chesley Sullenberger, still took over controls nonetheless and even pressed the override button. So that somehow is contrary to the normal rule, then.

It depends on the situation. Normally, Captains tend to take over controls if something goes wrong because ultimately they are responsible for the safety of the aircraft. For example, in the case of US Airways flight 1549, first officer Skiles was the PF, but the Captain (Sully) took over when they hit the birds. It eventually lead to a successful outcome. Most recently, we saw the same thing on United Airlines flight 1175.


text:
Were flight crew allowed to carry firearms before 9/11?
After the devastating terrorist attacks on September 11, 2001, many aspects of aviation safety and security were improved and/or enforced.
These security measures and enhancements include:

More complete and effective security checks in the airport
Reinforced cockpit doors
Strict regulations that forbid any non-flight crew member to enter the cockpit in flight
Probititation on flight crew opening the cockpit door due to demands or threats by terrorists

Another reaction to the terrorist attacks was the Federal Flight Deck Officer (FFDO) program, which allows federally approved, fully trained and licensed pilots to carry firearms in the cockpit.
However, in the Wikipedia article  states that:

Pilots are now allowed to carry firearms, but they must be trained and licensed.

Where  the use of the word "now" doesn't explicitly state that it was originally forbidden.
Likewise, the article on FFDO states that

Following the September 11 attacks in 2001, the Arming Pilots Against Terrorism Act, part of the Homeland Security Act of 2002, directed the Transportation Security Administration to develop the Federal Flight Deck Officer program as an additional layer of security.

Which only conveys the message that the FFDO program was initiated after 9/11, and also doesn't directly state that carrying firearms was illegal before 9/11.
Before 9/11, was it illegal for a pilot, who is also a fully trained and qualified legal firearm user to carry it in the cockpit?

@Jamiec In this post, I found the two Wikipedia pages that I find most relevant, so I included them here and also explains why they didn't solve my problem. And indeed no one complain about lack of research now, but this time it's of too much detail, so I'm wondering, what amount/type of research should I include? I would appreciate any advice, as I'm really puzzled now. (Note: I got around 60 downvotes (worth ~120 points) due to that lack of research thing, so you can see why I'm irritated and overcompensating here).

I would suggest you read some highly upvoted questions on topics that interest you to get a feel for how much detail to provide in your question.

I've reworked this question. Important points: 1) Some structure, using bullets, quotes, etc. 2) I didnt actually remove many words, just the fluff around them. 3) What I did remove was commentary, and hopefully keeps your question intact

When KLM began flying to Tokyo from Amsterdam in 1958, the route took them via Anchorage and then over the top of the world. The plane was a DC-7C, PH-DSC "Yellow Sea", and would be carrying 100 passengers.
KLM took into consideration the hazards that would face them following a forced landing, which included polar bear attack, and so purchased five or six ArmaLite AR-10 rifles for use on the Polar Route flights.

KLM gave transpolar flight crews survival training and presumably some
guidance on weapons handling but no actual trigger time with the
rifles instead advising them to simply aim between an attacking polar
bear’s shoulder blades.
source

Further details of the survival kit, including unique four-person sleeping-bags, maps, tissues, tents, a raft, a shovel, snow shoes, a small camp stove, candles, cold weather clothes, a hatchet and a saw can be found here.

The crew of the "Yellow Sea" prior to flying over the arctic from Anchorage to Tokyo, November 1958.

KLM stewardess (Puck Rijpstra?) with an AR-10 rifle during training before the polar flights.